=encoding UTF-8
=head1 Name
sqitchtutorial-exasol - A tutorial introduction to Sqitch change management on Exasol
=head1 Synopsis
sqitch *
=head1 Description
This tutorial explains how to create a sqitch-enabled Exasol project, use a
VCS for deployment planning, and work with other developers to make sure
changes remain in sync and in the proper order.
We'll start by creating a new project from scratch, a fictional antisocial
networking site called Flipr. All examples use L as
the VCS and L as the storage engine, but for
the most part you can substitute other VCSes and database engines in the
examples as appropriate.
If you'd like to manage a PostgreSQL database, see L.
If you'd like to manage an SQLite database, see L.
If you'd like to manage an Oracle database, see L.
If you'd like to manage a MySQL database, see L.
If you'd like to manage a Firebird database, see L.
If you'd like to manage a Vertica database, see L.
If you'd like to manage a Snowflake database, see L.
=head2 Connection Configuration
Sqitch requires ODBC to connect to the Exasol database. As such, you'll need
to make sure that the Exasol ODBC driver is properly configured. At its
simplest, on Unix-like systems, name the driver "Exasol" by adding this entry
to C (usually found in C, C, or
C):
[Exasol]
Description = ODBC for Exasol
Driver = /opt/EXASOL_ODBC-6.0.4/lib/linux/x86_64/libexaodbc-uo2214lv2.so
Note that you'll need to adjust the path depending on the version of the ODBC
driver, and where you installed it.
You might also consider naming your database connection by putting an entry in
C<~/.odbc.ini>, like so (assuming that Exasol is running on your local host):
[flipr_test]
Driver = Exasol
EXAHOST = 127.0.0.1:8563
EXAUID = sys
EXAPWD = exasol
Putting user and password information here is optional, but probably safer than
other available options as long as the file is protected (mode 0600) so that
only you can read it.
Normally, of course, you'd have a separate user per project (and a separate
ODBC connection defined); the above example is taken from the simplified
tutorial setup we're using.
See the
L for
ODBC drivers, documentation, etc.
=head2 Database Setup
While installing and configuring an Exasol instance is beyond the scope of this
tutorial, if you just want to follow along, you can start a Docker instance:
> docker run --detach --privileged --stop-timeout 120 -p 127.0.0.1:8563:8888 exasol/docker-db:latest
This will make Exasol available at 127.0.0.1 (localhost) on port 8563, as if
you were running it directly on your machine. You may have to wait for a minute
until the database finished initializing; you can try connecting with `exaplus`
to check status.
See the corresponding L
for more information about how to run Exasol using Docker, for example if you
want your data to persist beyond the lifetime of the container, etc.
=head1 Starting a New Project
Usually the first thing to do when starting a new project is to create a
source code repository. So let's do that with Git:
> mkdir flipr
> cd flipr
> git init .
Initialized empty Git repository in /flipr/.git/
> touch README.md
> git add .
> git commit -am 'Initialize project, add README.'
If you're a Git user and want to follow along the history, the repository
used in these examples is
L.
Now that we have a repository, let's get started with Sqitch. Every Sqitch
project must have a name associated with it, and, optionally, a unique URI. We
recommend including the URI, as it increases the uniqueness of object
identifiers internally, and will prevent the deployment of a different project
with the same name. So let's specify one when we initialize Sqitch:
> sqitch init flipr --uri https://github.com/sqitchers/sqitch-exasol-intro/ --engine exasol
Created sqitch.conf
Created sqitch.plan
Created deploy/
Created revert/
Created verify/
Let's have a look at F:
> cat sqitch.conf
[core]
engine = exasol
# plan_file = sqitch.plan
# top_dir = .
# [engine "exasol"]
# target = db:exasol:
# registry = sqitch
# client = exaplus
Good, it picked up on the fact that we're creating changes for the Exasol
engine, thanks to the C<--engine exasol> option, and saved it to the
file. Furthermore, it wrote a commented-out C<[engine "exasol"]> section with
all the available Exasol engine-specific settings commented out and ready to
be edited as appropriate.
By default, Sqitch will read F in the current directory for
settings. But it will also read F<~/.sqitch/sqitch.conf> for user-specific
settings. Since Exasol's C client is not in the path on my system,
let's go ahead an tell it where to find the client on our computer (don't
bother if you're using the
L because it uses the
client inside the container, not on your host machine):
> sqitch config --user engine.exasol.client /opt/EXAplus/exaplus
And let's also tell it who we are, since this data will be used in all
of our projects:
> sqitch config --user user.name 'Marge N. O’Vera'
> sqitch config --user user.email 'marge@example.com'
Have a look at F<~/.sqitch/sqitch.conf> and you'll see this:
> cat ~/.sqitch/sqitch.conf
[engine "exasol"]
client = /opt/EXAplus/exaplus
[user]
name = Marge N. O’Vera
email = marge@example.com
Which means that Sqitch should be able to find C for any project, and
that it will always properly identify us when planning and committing changes.
Back to the repository. Have a look at the plan file, F:
> cat sqitch.plan
%syntax-version=1.0.0
%project=flipr
%uri=https://github.com/sqitchers/sqitch-exasol-intro/
Note that it has picked up on the name and URI of the app we're building.
Sqitch uses this data to manage cross-project dependencies. The
C<%syntax-version> pragma is always set by Sqitch, so that it always knows how
to parse the plan, even if the format changes in the future.
Let's commit these changes and start creating the database changes.
> git add .
> git commit -am 'Initialize Sqitch configuration.'
[main a42564d] Initialize Sqitch configuration.
2 files changed, 16 insertions(+), 0 deletions(-)
create mode 100644 sqitch.conf
create mode 100644 sqitch.plan
=head1 Our First Change
First, our project will need a schema. This creates a nice namespace for all
of the objects that will be part of the flipr app. Run this command:
> sqitch add appschema -n 'Add schema for all flipr objects.'
Created deploy/appschema.sql
Created revert/appschema.sql
Created verify/appschema.sql
Added "appschema" to sqitch.plan
The L|sqitch-add> command adds a database change to the plan and writes
deploy, revert, and verify scripts that represent the change. Now we edit
these files. The C script's job is to create the schema. So we add
this to F:
CREATE SCHEMA flipr;
The C script's job is to precisely revert the change to the deploy
script, so we add this to F:
DROP SCHEMA flipr;
Now we can try deploying this change. We tell Sqitch where to send the change
via a L, assuming the default
C user and an ODBC driver named C (see
L for details):
> sqitch deploy 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
Adding registry tables to db:exasol://sys:@localhost:8563/?Driver=Exasol
Deploying changes to db:exasol://sys:@localhost:8563/?Driver=Exasol
+ appschema .. ok
(If you see an error resolving the TLS certificate, you can disable
certificate verification by adding C<&SSLCERTIFICATE=SSL_VERIFY_NONE> to the
end of the URL. Only do this for testing!)
First Sqitch created registry tables used to track database changes. The
structure and name of the registry varies between databases (Exasol uses a
schema to namespace its registry, while SQLite and MySQL use separate
databases). Next, Sqitch deploys changes. We only have one so far; the C<+>
reinforces the idea that the change is being C to the database.
With this change deployed, if you connect to the database, you'll be able to
see the schema:
> exaplus -q -u sys -p exasol -c localhost:8563 -sql "select schema_name from exa_schemas;"
SCHEMA_NAME
--------------------------------------------------------------------------------------------------------------------------------
SQITCH
FLIPR
=head2 Trust, But Verify
But that's too much work. Do you really want to do something like that after
every deploy?
Here's where the C script comes in. Its job is to test that the deploy
did was it was supposed to. It should do so without regard to any data that
might be in the database, and should throw an error if the deploy was not
successful. In Exasol, the simplest way to do so for schema is probably to
simply create an object in the schema. Put this SQL into
F:
CREATE TABLE flipr.verify__ (id int);
DROP TABLE flipr.verify__;
In truth, you can use I query that generates an SQL error if the schema
doesn't exist. Another handy way to do that is to divide by zero if an object
doesn't exist. For example, to throw an error when the C schema does
not exist, you could do something like this:
SELECT 1/COUNT(*) FROM exa_schemas WHERE schema_name = 'FLIPR';
Either way, run the C script with the L|sqitch-verify>
command:
> sqitch verify 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
Verifying db:exasol://sys:@localhost:8563/?Driver=Exasol
* appschema .. ok
Verify successful
Looks good! If you want to make sure that the verify script correctly dies if
the schema doesn't exist, temporarily change the schema name in the script to
something that doesn't exist, something like:
CREATE TABLE nonesuch.verify__ (id int);
Then L|sqitch-verify> again:
> sqitch verify 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
Verifying db:exasol://sys:@localhost:8563/?Driver=Exasol
* appschema .. Error: [42000] schema NONESUCH not found [line 1, column 40] (Session: 1582884049218108749)
# Verify script "verify/appschema.sql" failed.
not ok
Verify Summary Report
---------------------
Changes: 1
Errors: 1
Verify failed
It's even nice enough to tell us what the problem is. Or, for the
divide-by-zero example, change the schema name:
SELECT 1/COUNT(*) FROM exa_schemas WHERE schema_name = 'nonesuch';
Then the verify will look something like:
> sqitch verify 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
Verifying db:exasol://sys:@localhost:8563/?Driver=Exasol
* appschema .. Error: [22012] data exception - division by zero (Session: 1582884446489810101)
# Verify script "verify/appschema.sql" failed.
not ok
Verify Summary Report
---------------------
Changes: 1
Errors: 1
Verify failed
Less useful error output, but enough to alert us that something has gone
wrong.
Don't forget to change the schema name back before continuing!
=head2 Status, Revert, Log, Repeat
For purely informational purposes, we can always see how a deployment was
recorded via the L|sqitch-status> command, which reads the registry
tables from the database:
> sqitch status 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
# On database db:exasol://sys:@localhost:8563/?Driver=Exasol
# Project: flipr
# Change: f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
# Name: appschema
# Deployed: 2014-09-04 15:26:28 -0700
# By: Marge N. O’Vera
#
Nothing to deploy (up-to-date)
Let's make sure that we can revert the change:
> sqitch revert 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
Revert all changes from db:exasol://sys:@localhost:8563/?Driver=Exasol? [Yes]
- appschema .. ok
The L|sqitch-revert> command first prompts to make sure that we
really do want to revert. This is to prevent unnecessary accidents. You can
pass the C<-y> option to disable the prompt. Also, notice the C<-> before the
change name in the output, which reinforces that the change is being
I from the database. And now the schema should be gone:
> exaplus -q -u sys -p exasol -c localhost:8563 -sql "select schema_name from exa_schemas;"
SCHEMA_NAME
--------------------------------------------------------------------------------------------------------------------------------
SQITCH
And the status message should reflect as much:
> sqitch status 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
# On database db:exasol://sys:@localhost:8563/?Driver=Exasol
No changes deployed
Of course, since nothing is deployed, the L|sqitch-verify> command
has nothing to verify:
> sqitch verify 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
Verifying db:exasol://sys:@localhost:8563/?Driver=Exasol
No changes deployed
However, we still have a record that the change happened, visible via the
L|sqitch-log> command:
> sqitch log 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
On database db:exasol://sys:@localhost:8563/?Driver=Exasol
Revert f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
Name: appschema
Committer: Marge N. O’Vera
Date: 2014-09-04 16:33:02 -0700
Add schema for all flipr objects.
Deploy f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
Name: appschema
Committer: Marge N. O’Vera
Date: 2014-09-04 15:26:28 -0700
Add schema for all flipr objects.
Note that the actions we took are shown in reverse chronological order, with
the revert first and then the deploy.
Cool. Now let's commit it.
> git add .
> git commit -m 'Add flipr schema.'
[main 9bee4bd] Add flipr schema.
5 files changed, 197 insertions(+), 0 deletions(-)
create mode 100644 deploy/appschema.sql
create mode 100644 revert/appschema.sql
create mode 100644 sqitch.sql
create mode 100644 verify/appschema.sql
And then deploy again. This time, let's use the C<--verify> option, so that
the C script is applied when the change is deployed:
> sqitch deploy --verify 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
Deploying changes to db:exasol://sys:@localhost:8563/?Driver=Exasol
+ appschema .. ok
And now the schema should be back:
> exaplus -q -u sys -p exasol -c localhost:8563 -sql "select schema_name from exa_schemas;"
SCHEMA_NAME
--------------------------------------------------------------------------------------------------------------------------------
SQITCH
FLIPR
When we look at the status, the deployment will be there:
> sqitch status 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
# On database db:exasol://sys:@localhost:8563/?Driver=Exasol
# Project: flipr
# Change: fef4c2911ae68aee8f6ea164293a32923dc13b67
# Name: appschema
# Deployed: 2014-09-04 16:37:38 -0700
# By: Marge N. O’Vera
#
Nothing to deploy (up-to-date)
=head1 On Target
I'm getting a little tired of always having to type
C, aren't
you? This L tells
Sqitch how to connect to the deployment target, but we don't have to keep
using the URI. We can name the target:
> sqitch target add flipr_test 'db:exasol://sys:exasol@localhost:8563/?Driver=Exasol'
The L|sqitch-target> command, inspired by
L|https://git-scm.com/docs/git-remote>, allows management of one
or more named deployment targets. We've just added a target named
C, which means we can use the string C for the target,
rather than the URI. But since we're doing so much testing, we can also tell
Sqitch to deploy to the C target by default:
> sqitch engine add exasol flipr_test
Now we can omit the target argument altogether, unless we need to deploy to
another database. Which we will, eventually, but at least our examples will be
simpler from here on in, e.g.:
> sqitch status
# On database flipr_test
# Project: flipr
# Change: f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
# Name: appschema
# Deployed: 2014-09-04 16:37:38 -0700
# By: Marge N. O’Vera
#
Nothing to deploy (up-to-date)
Yay, that allows things to be a little more concise. Let's also make sure that
changes are verified after deploying them:
> sqitch config --bool deploy.verify true
> sqitch config --bool rebase.verify true
We'll see the L|sqitch-rebase> command a bit later. In the meantime,
let's commit the new configuration and and make some more changes!
> git commit -am 'Set default deployment target and always verify.'
[main 469779a] Set default deployment target and always verify.
1 files changed, 8 insertions(+), 0 deletions(-)
=head1 Deploy with Dependency
Let's add another change, this time to create a table. Our app will need
users, of course, so we'll create a table for them. First, add the new change:
> sqitch add users --requires appschema -n 'Creates table to track our users.'
Created deploy/users.sql
Created revert/users.sql
Created verify/users.sql
Added "users [appschema]" to sqitch.plan
Note that we're requiring the C change as a dependency of the new
C change. Although that change has already been added to the plan and
therefore should always be applied before the C change, it's a good
idea to be explicit about dependencies.
Now edit the scripts. When you're done, F should look like
this:
-- Deploy flipr:users to exasol
-- requires: appschema
CREATE TABLE flipr.users (
nickname VARCHAR(64) PRIMARY KEY,
password VARCHAR(256) NOT NULL,
fullname VARCHAR(256) NOT NULL,
twitter VARCHAR(256) NOT NULL,
ts TIMESTAMP WITH LOCAL TIME ZONE DEFAULT NOW() NOT NULL
);
COMMIT;
A few things to notice here. On the second line, the dependence on the
C change has been listed. This doesn't do anything, but the default
C Exasol template lists it here for your reference while editing
the file. Useful, right?
The table itself will be created in the C schema. This is why we need
to require the C change.
Now for the verify script. The simplest way to check that the table was
created and has the expected columns without touching the data? Just select
from the table with a false C clause. Add this to F:
SELECT nickname, password, fullname, twitter, ts
FROM flipr.users
WHERE FALSE;
Now for the revert script: all we have to do is drop the table. Add this to
F:
DROP TABLE flipr.users;
Couldn't be much simpler, right? Let's deploy this bad boy:
> sqitch deploy
Deploying changes to flipr_test
+ users .. ok
We know, since verification is enabled, that the table must have been created.
But for the purposes of visibility, let's have a quick look:
> exaplus -q -u sys -p exasol -c localhost:8563 -sql "describe flipr.users;"
COLUMN_NAME SQL_TYPE NULLABLE DISTRIBUTION_KEY
-------------------------------------------------------------------------------------------------------------------------------- ---------------------------------------- -------- ----------------
NICKNAME VARCHAR(64) UTF8 FALSE FALSE
PASSWORD VARCHAR(256) UTF8 FALSE FALSE
FULLNAME VARCHAR(256) UTF8 FALSE FALSE
TWITTER VARCHAR(256) UTF8 FALSE FALSE
TS TIMESTAMP WITH LOCAL TIME ZONE FALSE FALSE
We can also verify all currently deployed changes with the
L|sqitch-verify> command:
> sqitch verify
Verifying flipr_test
* appschema .. ok
* users ...... ok
Verify successful
Now have a look at the status:
> sqitch status
# On database flipr_test
# Project: flipr
# Change: 794a6c78816543909d592e2e9f5c0fade5b47406
# Name: users
# Deployed: 2017-11-02 11:02:40 +0100
# By: Marge N. O’Vera
#
Nothing to deploy (up-to-date)
Success! Let's make sure we can revert the change, as well:
> sqitch revert --to @HEAD^ -y
Reverting changes to appschema from flipr_test
- users .. ok
Note that we've used the C<--to> option to specify the change to revert to.
And what do we revert to? The symbolic tag C<@HEAD>, when passed to
L|sqitch-revert>, always refers to the last change deployed to the
database. (For other commands, it refers to the last change in the plan.)
Appending the caret (C<^>) tells Sqitch to select the change I to the
last deployed change. So we revert to C, the penultimate change.
The other potentially useful symbolic tag is C<@ROOT>, which refers to the
first change deployed to the database (or in the plan, depending on the
command).
Back to the database. The C table should be gone but the C schema
should still be around:
> exaplus -q -u sys -p exasol -c localhost:8563 -sql "describe flipr.users;"
Error: [42000] table or view FLIPR.USERS not found [line 1, column 10] (Session: 1582958508294847446)
The L|sqitch-status> command politely informs us that we have
undeployed changes:
> sqitch status
# On database flipr_test
# Project: flipr
# Change: f9759f0ed77964b6a3b6c7aa3b6058b4bb7db764
# Name: appschema
# Deployed: 2014-09-04 16:37:38 -0700
# By: Marge N. O’Vera
#
Undeployed change:
* users
As does the L|sqitch-verify> command:
> sqitch verify
Verifying flipr_test
* appschema .. ok
Undeployed change:
* users
Verify successful
Note that the verify is successful, because all currently-deployed changes are
verified. The list of undeployed changes (just "users" here) reminds us about
the current state.
Okay, let's commit and deploy again:
> git add .
> git commit -am 'Add users table.'
[main c7c24c5] Add users table.
4 files changed, 18 insertions(+), 0 deletions(-)
create mode 100644 deploy/users.sql
create mode 100644 revert/users.sql
create mode 100644 verify/users.sql
> sqitch deploy
Deploying changes to flipr_test
+ users .. ok
Looks good. Check the status:
> sqitch status
# On database flipr_test
# Project: flipr
# Change: d647ac8c130a7e0b12c9049789e46afb4a4f6e53
# Name: users
# Deployed: 2014-09-04 17:42:53 -0700
# By: Marge N. O’Vera
#
Nothing to deploy (up-to-date)
Excellent. Let's do some more!
=head1 Add Two at Once
Let's add a couple more changes. Our app will need to store status messages
from users. Let's call them -- and the table to store them -- "flips". And
we'll also need a view that lists user names with their flips. Let's add
changes for them both:
> sqitch add flips -r appschema -r users -n 'Adds table for storing flips.'
Created deploy/flips.sql
Created revert/flips.sql
Created verify/flips.sql
Added "flips [appschema users]" to sqitch.plan
> sqitch add userflips -r appschema -r users -r flips \
-n 'Creates the userflips view.'
Created deploy/userflips.sql
Created revert/userflips.sql
Created verify/userflips.sql
Added "userflips [appschema users flips]" to sqitch.plan
Now might be a good time to have a look at the deployment plan:
> cat sqitch.plan
%syntax-version=1.0.0
%project=flipr
%uri=https://github.com/sqitchers/sqitch-exasol-intro/
appschema 2014-09-04T18:40:34Z Marge N. O’Vera # Add schema for all flipr objects.
users [appschema] 2014-09-04T23:40:15Z Marge N. O’Vera # Creates table to track our users.
flips [appschema users] 2014-09-05T00:16:58Z Marge N. O’Vera # Adds table for storing flips.
userflips [appschema users flips] 2014-09-05T00:18:43Z Marge N. O’Vera # Creates the userflips view.
Each change appears on a single line with the name of the change, a bracketed
list of dependencies, a timestamp, the name and email address of the user who
planned the change, and a note.
Let's write the code for the new changes. Here's what F
should look like:
-- Deploy flipr:flips to exasol
-- requires: appschema
-- requires: users
CREATE TABLE flipr.flips (
id INTEGER IDENTITY PRIMARY KEY,
nickname VARCHAR(64) NOT NULL REFERENCES flipr.users(nickname),
body VARCHAR(180) DEFAULT '' NOT NULL,
ts TIMESTAMP WITH LOCAL TIME ZONE DEFAULT NOW() NOT NULL
);
COMMIT;
Here's what F might look like:
-- Verify flipr:flips on exasol
SELECT id, nickname, body, ts
FROM flipr.flips
WHERE FALSE;
ROLLBACK;
And F should look something like this:
-- Revert flipr:flips from exasol
DROP TABLE flipr.flips;
COMMIT;
Now for C; F might look like this:
-- Deploy flipr:userflips to exasol
-- requires: appschema
-- requires: users
-- requires: flips
CREATE OR REPLACE VIEW flipr.userflips AS
SELECT f.id, u.nickname, u.fullname, f.body, f.ts
FROM flipr.users u
JOIN flipr.flips f ON u.nickname = f.nickname;
COMMIT;
Use a C